Chelone

Introduction

Chelone is an interpreter for a subset of the Logo programming language (mostly the turtle parts) implemented in chevrotain.

Usage

• npm install
• Example: npm run turtle -- -P "to spiral :length if :length > 300 [stop] forward :length right 10 spiral :length * 1.05 end spiral 1" -O output.svg
  • If run without options (npm run turtle), will output a demo image to turtle.svg

Implemented Commands

If you're not familiar with Logo or turtle graphics, check out the Logo Foundation's Logo Primer.

Drawing and Movement

• penup (alias pu)
• pendown (alias pd)
• forward <amount> (alias fd)
• backward <amount> (alias bk)
• right <degrees> (alias rt)
• left <degrees> (alias lt)
• home
• setxy <x> <y> (relative to the origin)

Iteration, Procedures, Variables

• repeat <count> [<statements>]
• to <procedure> :<inputA> :<inputB> :<inputC> <statements> end
• make "<variable> <value>

Conditionals and Flow Control

• if <valueA> = <valueB> [<statements>]
  • =, !=, >, <
• stop in a repeat or procedure to end execution
• output in a procedure to return a value

Calculation

• +, -, *, /, unary -
• random <max> (random integer from 0 to max exclusive)

Chelone?

In Greek myth, Chelone was a nymph who was turned into a tortoise because she didn't RSVP to Zeus and Hera's wedding.